Battery system configured to survive failure of one or more batteries

ABSTRACT

The battery system includes a battery pack having a plurality of power sources arranged in parallel groups that are connected in series. Each parallel group includes a plurality of power sources connected in parallel. Each power source includes a battery. The system also includes electronics configured to repeatedly charge the battery pack according to a charging protocol. The charging protocol is configured such that the voltage of any one battery in the battery pack does not exceed its maximum operational voltage after failure of a battery in the battery pack.

RELATED APPLICATIONS

This Application is a continuation of U.S. patent application Ser. No.11/501,095, filed on Aug. 8, 2006, entitled “Battery System Configuredto Survive Failure of One or More Batteries;” which claims the benefitof U.S. Provisional Patent Application Ser. No. 60/740,150, filed onNov. 28, 2005, entitled “Battery System Configured to Survive Failure ofOne or More Batteries;” each of which is incorporated herein in itsentirety.

FIELD

The present invention relates to electrochemical devices and moreparticularly to battery packs.

BACKGROUND

Rechargeable battery packs have been proposed, however, one or more ofthe batteries in these battery packs can fail. For instance, one or moreof the batteries can experience an internal failure such as a short, cantrigger a safety device such as a burst disc and/or can becomeelectrically disconnected from the other batteries. Recharging a batterypack after failure of a battery can increase the voltage one or more ofthe remaining batteries above its maximum operational voltage.Additionally, discharging a battery pack after failure of a battery candecrease the voltage one or more of the remaining batteries below itsminimum operational voltage. Accordingly, charging and/or recharging abattery pack after failure of a battery can cause failure of otherbatteries in the battery pack and can accordingly cause failure of theentire battery pack. As a result, there is a need for a battery systemthat permits cycling of the battery pack after failure of a battery.

SUMMARY

A method of operating a battery pack is disclosed. The battery pack hasa plurality of parallel groups connected in series. Each parallel groupincludes a plurality of power sources connected in parallel. Each powersource includes a battery. The method includes repeatedly charging thebattery pack according to a charging protocol. The charging protocol isconfigured such that the voltage of any one battery in the battery packdoes not exceed its maximum operational voltage after failure of abattery in the battery pack. The charging protocol can include chargingthe battery pack to a charged pack voltage. The charged pack voltage canremain the same after a battery fails as before the battery fails.

Another embodiment of the method includes repeatedly discharging thebattery pack according to a charging protocol. The charging protocol isconfigured such that the voltage of any one battery in the battery packdoes not fall below its minimum operational voltage after failure of abattery in the battery pack. The charging protocol can includedischarging the battery pack to a discharged pack voltage. Dischargingthe battery pack to a discharged pack voltage can include or consist ofstopping discharge of the battery pack when the pack voltage falls tothe discharged pack voltage. The discharged pack voltage can remain thesame after a battery fails as before the battery fails.

Another embodiment of the method includes repeatedly charging anddischarging the battery pack according to a charging protocol. Thecharging protocol can be the same after a battery fails as before thebattery fails. The charging protocol can be selected such that such thatthe voltage of any one battery in the battery pack does not exceed itsmaximum operational voltage after failure of a battery in the batterypack and such that the voltage of any one battery in the battery packdoes not fall below its minimum operational voltage after failure of abattery in the battery pack. In some instances, the capacity dischargedfrom each battery when discharging the battery pack from the chargedpack voltage to the discharged pack voltage before failure of thebattery is less than or equal to C_(m)(M−1)/(M+1), where M is the numberof power sources in each parallel group and C_(m) is the maximumoperational capacity of a battery.

A battery system is disclosed. The battery system includes electronicsin electrical communication with the battery pack. The electronics canbe configured to control and/or monitor the charging and/or dischargingof the battery pack according to the disclosed methods.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram of a battery system including electronicsfor controlling and/or monitoring the charging and/or discharging of abattery pack.

FIG. 2A is a schematic diagram of a battery pack. The battery packincludes a plurality of power sources arranged in parallel groups andseries groups. Each parallel group includes a plurality of power sourcesconnected in parallel. Each series group connects a power source fromeach of the parallel groups in series.

FIG. 2B is an alternate schematic for the batteries in the battery packof FIG. 2A.

FIG. 3A illustrates a voltage versus charge capacity curve for a batterysuitable for use in a battery pack according to FIG. 2A or FIG. 2B.

FIG. 3B illustrates a voltage versus charge capacity curve for a batterysuitable for use in a battery pack according to FIG. 2A or FIG. 2B.

DESCRIPTION

A battery system having electronics and a battery pack is disclosed. Theelectronics are configured to monitor and/or control the charge and/orthe discharge of the battery pack. The battery pack includes a pluralityof power sources that each includes a battery. The power sources arearranged in parallel groups that are connected in series. Each parallelgroup includes a plurality of power sources connected in parallel.

The electronics are configured to repeatedly charge and/or discharge thebattery pack according to a charging protocol. The charging protocol isconfigured such that after failure of a battery in the battery pack, thevoltage to which each of the batteries is charged is less than or equalto its maximum operational voltage and/or the voltage to which each ofthe batteries is discharged is greater than or equal to its minimumoperational voltage. As a result, the failure of one of the batteries inthe battery pack does not create a risk of failure of the batteriesremaining in the battery pack.

FIG. 1 provides a schematic illustration of a battery system. Thebattery system includes electronics 8 in electrical communication with abattery pack 10 and with the terminals 11 for the battery system. Theelectronics can be incorporated into the battery pack or can be externalfrom the battery pack. The electronics are configured to control and/ormonitor the discharge and charge of the battery pack. Suitableelectronics include, but are not limited to, firmware, hardware andsoftware or a combination thereof. Examples of suitable electronicsinclude, but are not limited to, analog electrical circuits, digitalelectrical circuits, processors, microprocessors, digital signalprocessors (DSPs), computers, microcomputers, ASICs, and discreteelectrical components, or combinations suitable for performing therequired control functions. In some instances, the electronics includeone or more memories and one or more processing units such as a CPU. Theone or more memories can include instructions to be executed by theprocessing unit during performance of the control and monitoringfunctions. Although not illustrated, the electronics can include or beattachable to a power source that provides power for charging thebattery pack.

FIG. 2A provides a schematic diagram of the battery pack 10. The batterypack includes two primary parallel lines 12 that connect three seriesgroups 14 in parallel. The series groups 14 each include three powersources 16 connected in series. Primary series lines 18 each provideelectrical communication between a series group 14 and a primaryparallel line 12 and secondary series lines 20 provide electricalcommunication between the power sources 16 connected in series.

The battery pack also includes a plurality of secondary parallel lines22. The secondary parallel lines 22 each include one or more cross lines24 that provide electrical communication between the secondary serieslines 20 in different series groups 14. Accordingly, each secondaryparallel line 22 provides a parallel connection between the powersources 16 in different series group 14. For instance, each secondaryparallel line 22 provides electrical communication between differentseries groups 14 such that a power source 16 in one of the series groups14 is connected in parallel with a power source 16 in the other seriesgroups 14. Because a single secondary parallel line 22 only provides oneof the parallel connections, another connection is needed to connectpower sources 16 in parallel. The other parallel connection can beprovided by another secondary parallel line 22 or by a primary parallelline 12. Each of the power sources 16 connected in parallel belongs to aparallel group 28. Accordingly, the battery pack of FIG. 2A includesthree parallel groups 28.

The battery pack of FIG. 2A can also be illustrated as a plurality ofparallel groups connected in series as shown in FIG. 2B. In FIG. 2B, twoparallel lines 31 connected by a series line 33 replace the secondaryparallel lines of FIG. 2A. Accordingly, the battery pack excludes seriesgroups. The schematic of FIG. 2A may be preferable because all of thepack current must pass through the series lines of FIG. 2B. As a result,the series lines may need to be larger than other lines in the batterypack and accordingly may add weight to the battery pack. For instance,when the battery pack is configured to provide large current levels, theseries lines may each need to be a metal bar rather than a conventionalconductor such as a wire.

The assembly illustrated in FIG. 2A and/or FIG. 2B can be scaled toinclude more power sources or fewer power sources. For instance, thesystem can include four or more power sources, twelve or more powersources, twenty-five or more power sources, eighty-one or more powersources, one hundred or more power sources. The number of power sourcesin each parallel group can be the same or different from the number ofpower sources in each series group 14. The number of power sources ineach series group 14 can be increased in order to increase the voltageof the system or decreased in order to decrease the voltage of thesystem. Each series group 14 can include two or more power sources; fouror more power sources; more than eight power sources; or fifteen or morepower sources. The number of series groups 14 can be increased forapplications that require higher power levels or decreased forapplications that require lower power levels. In one embodiment, thebattery pack includes only one parallel group and no series groups. Thebattery pack module can include two or more series groups; four or moreseries groups; ten or more series groups; or fifteen or more seriesgroups 70. The battery pack can include two or more series groups 14;four or more series groups 14; ten or more series groups 14; or fifteenor more series groups 14.

The connections between the power sources can be standard methods forconnecting power sources. The connections between the power sources andthe conductors can be made using connection methods that are suitablefor the amount of current and power that will be delivered by thebattery. For instance, conductors can be connected to a power source bywelding. Additionally or alternately, one or more of the primaryparallel lines and the connected primary series lines can optionally beintegrated into a single line. For instance, a single wire, cable, pieceof sheet metal, or metal bar can serve as both a primary parallel lineand as the connected primary series lines. Additionally or alternately,one or more the secondary parallel lines and the connected secondaryseries lines can optionally be integrated into a single line. Forinstance, a single wire, cable, piece of sheet metal, or metal bar canserve as both a secondary parallel line and as the connected secondaryseries lines.

Although FIG. 2A illustrates the secondary parallel lines 22 providingelectrical communication between the series groups 14 such that a powersource 16 in one of the series groups 14 is connected in parallel with apower source 16 in each of the other series groups 14, the secondaryparallel lines 22 can provide electrical communication between theseries groups 14 such that a power source 16 in one of the series groups14 is connected in parallel with a power source 16 in a portion of theother series groups 14.

Although not illustrated in FIG. 2A and/or FIG. 2B, the battery pack caninclude other electrical connections between the primary parallel lines12. For instance, other power sources and/or series groups can beconnected between the primary parallel lines 12 but not otherwiseelectrically connected to the illustrated series groups. Further, thebattery pack can include other components. For instance, the batterypack can include fuses positioned such that if a battery shorts, thebattery is no longer in electrical communication with the rest of thebatteries in the battery pack. Accordingly, the fuses can prevent a cellthat shorts in a parallel group from shorting the other cells in theparallel group.

The battery pack can be configured to provide more than 9 V or more than12 V. Additionally or alternately, the battery packs can be configuredto provide more than 50 watt-hours, more than 100 watt-hours or morethan 240 watt-hours. Many of the advantages associated with the batterypack do not become evident until the battery pack is used forapplications requiring high power levels. As a result, the battery packis suitable for high power applications such as powering the movement ofvehicles such as trucks, cars and carts. For these high powerapplications, the battery pack is preferably configured to provide morethan 18 V, more than 24 V or more than 32 V. Additionally oralternately, the battery pack is preferably configured to provide morethan 240 watt-hours, more than 500 watt-hours or more than 1000watt-hours. In some instances, the above performance levels are achievedusing a battery pack where the batteries in the series groups 14 eachhave a voltage of less than 14 V, 10 V or 5 V. In some instances, thebattery pack is configured to provide a maximum current greater than 30A and includes two, three, or more than three series groups. In order tocarry this level of current, the primary parallel lines 12 generallymust be a metal bar rather than traditional connections such as wires.However, when the battery pack configuration of FIG. 2A is employed, thesecondary balance lines 22 may not need to be metal bars as disclosed inProvisional Patent Application Ser. No. 60/601,285. These metal bars canbe thick, expensive, and heavy. As a result, using conductors other thanmetal bars for the balance lines can reduce the costs, size and weightof the battery pack.

In some instances, one or more of the power sources are configured toprovide more than 9 V or more than 12 V. Additionally or alternately,the power sources can be configured to provide more than 50 watt-hours,more than 100 watt-hours or more than 240 watt-hours. When the batterypack is used for applications requiring high power levels such aspowering the movement of vehicles such as trucks, cars and carts, thepower sources are preferably configured to provide more than 18 V, morethan 24 V or more than 32 V. Additionally or alternately, the powersources are preferably configured to provide more than 240 watt-hours,more than 500 watt-hours or more than 1000 watt-hours.

Each of the power sources 16 includes one or more batteries. In someinstances, one or more of the power source 16 includes a plurality ofbatteries connected in parallel and/or one or more of the power source16 includes a plurality of batteries connected in series. The batteriesare preferably each the same physical size but can be different sizes.In some instances, one or more of the power sources includes or consistsof a battery pack. In some instances, each of the power sources includesor consists of a battery pack. In one example, the power sources eachare each a battery pack having a plurality of pack parallel groupsconnected in series where each pack parallel group includes a pluralityof batteries connected in parallel. Each battery pack can includeelectronics that charge and discharge the battery pack so as to survivefailure of one or more batteries using the methods described herein. Forinstance, the battery pack of FIG. 2A or FIG. 2B can be constructed suchthat each power source 16 is also constructed according to FIG. 2A orFIG. 2B with a battery serving as the power source 16. With thisconstruction, each of the power sources can optionally includeelectronics with all or a portion of the functions attributed to theelectronics 8 of FIG. 1. When a plurality of the power sources are abattery pack, the battery packs are preferably each the same size butcan be different sizes. A power source 16 or battery pack can includeelectrical components in addition to batteries. For instance, a powersource 16 can include one or more resistors and one or more capacitorsin addition to the one or more batteries. In a preferred embodiment,each of the power sources 16 consists of one or more batteries and theassociated electrical connections.

Additional details about the construction and operation of batterypacks, battery systems, batteries, and suitable electronics can be foundin U.S. Provisional Patent Application Ser. No. 60/601,285; filed onAug. 13, 2004; entitled “Battery Pack;” and in U.S. patent applicationSer. No. 11/201,987; filed on Aug. 10, 2005; and entitled “BatteryPack;” and in U.S. Patent Application Ser. No. 60/707,500; filed on Aug.10, 2005; and entitled “Battery System;” and in U.S. patent applicationSer. No. (Not yet assigned); filed on Nov. 28, 2005; and entitled“Battery Pack System;” and in U.S. patent application Ser. No. (Not yetassigned); filed on Nov. 28, 2005; and entitled “Battery Pack System;”and in U.S. patent application Ser. No. 11/269,285; filed on Nov. 8,2005; and entitled “Modular Battery Pack;” each of which is incorporatedherein in its entirety. When possible, the functions of the electronicsand/or controllers described in the above applications can be performedin addition to the functions described in this application. Theteachings in these applications can be applied to the battery system,battery packs, batteries, electronics, and methods of operationdisclosed in this application.

As noted above, the electronics of FIG. 1 are configured to monitorand/or control the charging and discharging of the battery pack. Each ofthe batteries has a maximum operational voltage above which it cannot becharged without subjecting the battery to failure. Additionally, each ofthe batteries has minimum operational voltage below which it cannot becharged without subjecting the battery to failure. The electronics cancontrol the charging of the battery pack such that the voltage of anyone cell does not exceed its maximum operational voltage after failureof a cell in the battery pack. Additionally or alternately, theelectronics can control the discharge of the battery pack such that thevoltage of any one cell does not fall below exceed its minimumoperational voltage after failure of a cell in the battery pack. As aresult, a battery in the battery pack can fail without causing failureof the entire battery pack.

The electronics employ a charging protocol to recharge the battery packto a charged pack voltage and/or to discharge the battery pack to adischarged pack voltage. The battery pack can be charged to the chargedpack voltage using constant current, constant voltage, and combinationsthereof and other suitable methods. The charging protocol can includeother steps and/or functions. For instance, the electronics can includea temperature-measuring device and the electronics can stop or slow thecharging of the battery pack in the event the temperature of the batterypack rises above a temperature threshold.

When the battery pack is charged to the charged pack voltage before abattery in the battery pack fails, each of the batteries is charged to acharged voltage before failure which may be the same or different fordifferent batteries in the battery pack. After a battery has failed andthe electronics use the same charging protocol to recharge the batterypack, each of the batteries is charged to a charged voltage afterfailure which may be the same or different for different batteries inthe battery pack. For at least one battery in the battery pack, thecharged voltage after failure is different from the charged voltagebefore failure. For instance, when the battery pack is constructedaccording to FIG. 2A and/or FIG. 2B, the failure of a battery in one ofthe parallel groups increases the portion of the charging current thatflows through the batteries that remain in the parallel group with thefailed battery. As a result, the batteries remaining in that parallelgroup will be charged to a higher voltage after failure than before thefailure. Batteries having a charged voltage after failure that exceedtheir maximum operational voltage are subject to failure and accordinglysubject the battery pack to failure.

The electronics can be configured to recharge the battery pack such thatafter failure of a battery, the battery pack can be recharged with thesame recharging protocol without any one of the batteries having acharged voltage after failure that exceeds its maximum operationalvoltage. For instance, the charged pack voltage can be less than themaximum operational voltage of the battery pack. The maximum operationalvoltage of a battery pack is the voltage of the battery pack when eachof the batteries is charged to its maximum operational voltage. Forinstance, a battery pack constructed according to FIG. 2A and/or FIG. 2Bhas a maximum operational voltage equal to the sum of the maximumoperational voltage of each parallel group. As a further example, abattery pack constructed according to FIG. 2A and/or FIG. 2B withbatteries that each have a maximum operational voltage of V_(m) arrangedin N parallel groups has a maximum operational voltage of N*V_(m).

The charging protocol can also be configured such that the chargedvoltage after failure for each battery is less than its maximumoperational voltage. For instance, the charging protocol employed by theelectronics can be the same before the failure of a battery and afterthe failure of a battery but can be configured so the charged voltageafter failure of each battery is less than or equal to the maximumoperational voltage for each battery. As a result, charging the batterypack after the failure does not cause other batteries in the batterypack to fail.

When the battery pack is discharged to the discharged pack voltagebefore a battery in the battery pack fails, each of the batteries isdischarged to a discharged voltage before failure which may be the sameor different for different batteries in the battery pack. After abattery has failed and the electronics use the same charging protocol todischarge the battery pack, each of the batteries is discharged to adischarged voltage after failure which may be the same or different fordifferent batteries in the battery pack. For at least one battery in thebattery pack, the discharged voltage after failure is different from thedischarged voltage before failure. For instance, when the battery packis constructed according to FIG. 2A and/or FIG. 2B, the failure of abattery in one of the parallel groups increases the portion of thedischarging current that flows from the batteries that remain in theparallel group with the failed battery. As a result, the batteriesremaining in that parallel group may be discharged to a lower voltageafter the failure than before the failure. Batteries having a dischargedvoltage after failure below their minimum operational voltage aresubject to failure and accordingly subject the battery pack to failure.

The electronics can be configured to discharge the battery pack suchthat after failure of a battery, the battery pack can be discharged withthe same charging protocol without any one of the batteries having adischarged voltage after failure that falls below its minimumoperational voltage. For instance, the discharged pack voltage can begreater than or equal to the minimum operational voltage of the batterypack. The minimum operational voltage of a battery pack is the voltageof the battery pack when each of the batteries is discharged to itsminimum operational voltage. For instance, a battery pack constructedaccording to FIG. 2A and/or FIG. 2B has a minimum operational voltageequal to the sum of the minimum operational voltage of each parallelgroup. As a further example, a battery pack constructed according toFIG. 2A and/or FIG. 2B with batteries that each have a minimumoperational voltage of V_(mi) arranged in N parallel groups has aminimum operational voltage of N*V_(mi).

The charging protocol can also be configured such that the chargedvoltage after failure for each battery is less than its minimumoperational voltage. For instance, the charging protocol employed by theelectronics can be the same before the failure of a battery and afterthe failure of a battery but can be configured so the discharged voltageafter failure of each battery is greater than or equal to the minimumoperational voltage for each battery. As a result, discharging thebattery pack after the failure does not cause other batteries in thebattery pack to fail.

An example of a suitable charging protocol can be generated byidentifying the maximum capacity range that the battery that remainintact in the battery pack may be required to provide after a battery inthe battery pack fails. The circuitry of the battery pack can beemployed to determine this maximum capacity range. When a battery packis constructed according to FIG. 2A or FIG. 2B and a battery in aparticular parallel group fails, the capacity that batteries in otherparallel groups will be required to provide will remain substantiallyunchanged. However, the capacity requirements of the batteries in thesame parallel group will increase by ΔC, where: ΔC=C_(f)−C_(o); C_(f) isthe charge capacity that the intact battery has after failure of theother battery; and Co is the capacity that that intact battery hadbefore the failure. An analysis of FIG. 2A and/or FIG. 2B shows thatC_(f)=C_(o)M/(M−1), where M is the number of series groups in thebattery pack or M is the number of power sources in each parallel group.Accordingly, ΔC=C_(o)/(M−1). As a result, the additional capacity thatwill be required by each battery that remains in the parallel group isC_(o)/(M−1).

Because a battery can fail at different points in the discharge/chargecycle of the battery pack, the additional capacity that is required ofthe batteries remaining intact in a parallel group, ΔC, can also berequired at different parts in the discharge/charge cycle. For instance,the total capacity values that will be required of the intact batterieswill be different if the battery fails after charging than will berequired if the battery fails after discharging. When cycling thebattery pack charges and discharges a battery between a dischargedcapacity of C₁ and a charged capacity C₂ and another battery in the sameparallel group fails after the battery pack is fully charged,discharging of the battery pack will decrease the capacity of theremaining intact battery to C₁−ΔC. This capacity can represent theminimum capacity value that the battery can reach after failure of abattery. When the same battery fails after discharging the battery pack,charging the battery pack will increase the remaining intact battery toC₂+ΔC. This capacity can represent the maximum capacity value that thebattery can reach after failure of the battery. As a result, the rangeof capacity values for the remaining intact battery can be expressed as(C₂+ΔC)−(C₁−ΔC). Because C₂−C₁=Co, the maximum capacity range for theremaining intact battery can be expressed as C_(o)+2ΔC or asC_(o)+2C_(o)/(M−1).

Each battery is associated with a maximum operational capacity, C_(m),which is the capacity discharged when discharging from its maximumoperational voltage to its minimum operational voltage. To ensure thatthe batteries do not exceed their maximum operational capacity after thefailure of a battery, the charging protocol is configured such that themaximum capacity range for the remaining intact battery is less than themaximum operational capacity of the battery. This condition can beexpressed as C_(o)+2C_(o)/(M−1)≦C_(m). Accordingly, the chargingprotocol is configured such that C_(o)≦C_(m)(M−1)/(M+1). C_(o) can beconfigured so as to be less than C_(m)(M−1)/(M+1) to provide additionalsafety buffer.

The C_(o) value can be compared to data indicating voltage as a functionof discharge capacity to determine a discharged pack capacity. FIG. 3Apresents an example of this data for a SONY 18650 cell. The data ispresented as a graph of voltage versus discharge capacity. These cellshave a maximum operational voltage of 4.2 V, a minimum operationalvoltage of 2.7 V and a maximum operational capacity of 1.28 Ah whendischarged from 4.2 V to 2.7 V when discharged at a rate of 1 C. Thevariables determined above are compared to FIG. 3A to identify adischarged battery voltage that allows a capacity buffer of ΔC on bothsides of the C_(o) value. For instance, as noted above, a battery mustbe capable of delivering additional capacity equal to ΔC both above andbelow the range of capacity values being provided by the battery beforea different battery fails. The additional capacities of ΔC are marked inFIG. 3A. The maximum capacity that can be discharged while preservingthe ΔC buffers above the range of capacity values is C_(m)−ΔC. Thevoltage corresponding to C_(m)−ΔC is labeled V_(D2) on FIG. 3A. Theminimum capacity that can be discharged while preserving the ΔC buffersis C_(o)+ΔC. The voltage corresponding to C_(o)+ΔC is labeled _(VD1) onFIG. 3A. The battery can be discharged to a voltage between V_(D1) andV_(D2) while preserving the ΔC buffers each end of the capacity range.As a result, a value for the discharged voltage before failure, labeledV_(BD), can be configured between V_(D1) and V_(D2). It may bepreferable to select a discharged voltage before failure at about theaverage of V_(D1) and V_(D2) or associated with the average of (C_(m)−ΔCand C_(o)+ΔC) in, order to provide additional buffer at both ends of thecapacity spectrum. In instances where C_(o)=C_(m)(M−1)/(M+1), V_(D1)will be equal to V_(D2) and the value for the battery voltage will equalV_(D1). The discharged pack voltage for use in the charging protocol canbe N*V_(BD) where N is the number of parallel groups in the batterypack.

The C_(o) value can be compared to data indicating voltage as a functionof charge capacity to determine a charged pack capacity. FIG. 3Bpresents an example of this data for the same cells that were employedin FIG. 3A. The data is presented as a graph of voltage versus chargecapacity. FIG. 3B was generated by using a constant current charge at1.3 Ah. The increase in the battery capacity that results from chargingis added to the battery discharge voltage is identified and compared tothe data in order to identify a value for the charged battery voltage,V_(BC). For instances, the charge capacity associated with thedischarged voltage before failure, V_(BD), is marked on FIG. 3B andlabeled C_(BD). The value of V_(BD)+C_(O) is also marked on FIG. 3B. Thevoltage associated with the capacity V_(BD)+C_(O) is identified andmarked V_(BC). This value of V_(BC) can serve as the charged voltagebefore failure, V_(BC). The charged pack voltage for use in the chargingprotocol can be N*V_(BC) where N is the number of parallel groups in thebattery pack. In some instances, the charging protocol includes chargingthe battery pack to the charged pack voltage represented by N*V_(BC) anddischarging the battery pack to the discharged pack voltage representedby N*V_(BD).

The charging protocol presented above provides an advantage of lowlevels of capacity loss in the event that a battery does fail. Further,because C_(o)≦C_(m)(M−1)/(M+1), as noted above, the value of Co canapproach Cm very quickly as the value of M increases. As a result,increasing the number of series groups quickly permits the value of Coto approach the maximum operational capacity of the batteries, C_(m).

The maximum operational voltage for a battery can be function of thebattery application. For instance, the maximum operational voltagegenerally decreases as the desired number of cycles increases. As aresult, the maximum operational voltage is generally determined from thebattery specification. In the absence of specifications, the maximumoperational voltage is the voltage to which a battery can be chargedwhile still providing the desired cycling performance. Additionally, theminimum operational voltage for a battery can be a function of thebattery application. For instance, the minimum operational voltagegenerally increases as the desired number of cycles increases. As aresult, the minimum operational voltage is generally determined from thebattery specification. In the absence of specifications, the minimumoperational voltage is the voltage to which a battery can be dischargedwhile still providing the desired cycling performance.

Additional details about the construction, operation, and/or electronicsof the battery pack and the battery system can be found in U.S.Provisional Patent Application Ser. No. 60/601,285; filed on Aug. 13,2004; entitled “Battery Pack;” and in U.S. patent application Ser. No.11/201,987; filed on Aug. 10, 2005; and entitled “Battery Pack;” and inU.S. Patent Application Ser. No. 60/707,500; filed on Aug. 10, 2005; andentitled “Battery System;” and in U.S. Provisional Patent ApplicationSer. No. 60/740,150; filed on Nov. 28, 2005; and entitled “BatterySystem Configured to Survive Failure of One or More Batteries;” and inU.S. Provisional Patent Application Ser. No. 60/740,202; filed on Nov.28, 2005; and entitled “Battery Pack System;” and in U.S. patentapplication Ser. No. 11/269,285; filed on Nov. 8, 2005; and entitled“Modular Battery Pack;” and in U.S. Provisional U.S. Patent ApplicationSer. No. 60/740,204, filed on Nov. 28, 2005, entitled “Battery PackSystem;” and in U.S. Provisional U.S. Patent Application Ser. No.60/753,862, filed on Dec. 22, 2005, entitled “ Battery Pack System;” andin U.S. Provisional Patent Application Ser. No. 60/819,421, filed onJul. 6, 2006, entitled “ Battery Pack System;” and in U.S. patentapplication Ser. No. 11/404,211, filed on Apr. 13, 2006, entitled“Battery Pack System;” and in U.S. patent application Ser. No. (not yetassigned), filed on Aug. 8, 2006, entitled “ Battery System;” each ofwhich is incorporated herein in its entirety. When possible, thefunctions of the electronics described in the above applications can beperformed by the electronics of this application in addition to thefunctions described in this application. In some instances, the batterypack and/or the battery system are constructed as disclosed in the aboveapplications and/or includes features described in the aboveapplication.

The battery pack disclosed in this Patent Application can be a batterypack system such as the battery pack system disclosed in U.S. PatentApplication Ser. No. 60/819,421. The battery pack system disclosed inU.S. Provisional U.S. Patent Application Ser. No. 60/819,421 includes aplurality of battery packs. Each of the individual battery packs in thebattery pack system can be operated as disclosed in this PatentApplication.

The function of the electronics is described above in the context ofdischarging the battery pack to a discharged pack voltage. However, inmany instances, the battery pack is charged before the battery packreaches the discharged pack voltage. Accordingly, the electronics may beconfigured to stop the discharge of the battery pack in the event thatthe pack voltage falls below the discharged pack voltage. As a resultthe discharged pack voltage may serve as a threshold at which theelectronics stop the discharge of the battery pack.

Although the above battery system is disclosed in the context of abattery pack where a single battery fails, the above principles can beextended to charging protocols for battery packs where multiplebatteries fail.

Other embodiments, combinations and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. Therefore, this invention is to be limited only by thefollowing claims, which include all such embodiments and modificationswhen viewed in conjunction with the above specification and accompanyingdrawings.

1. A battery system, comprising: a battery pack having a pluralityparallel groups connected in series, each parallel group including aplurality of power sources connected in parallel, each power sourceincluding a battery; and electronics configured to charge the batterypack according to a charging protocol configured such that the voltageof any one battery in the battery pack does not exceed its maximumoperational voltage after failure of a battery in the battery pack. 2.The system of claim 1, wherein the electronics are configured torecharge the battery pack with the same charging protocol before failureof the battery and after failure of the battery.
 3. The system of claim2, wherein the charging protocol includes charging the battery pack to acharged pack voltage, the charged pack voltage being the same before andafter the failure of the battery.
 4. The system of claim 1, wherein eachpower source consists of a battery.
 5. The system of claim 1, whereinthe charging protocol discharges the battery pack such that the voltageof any one battery in the battery pack does not fall below its minimumoperational voltage after failure of a battery in the battery pack. 6.The system of claim 1, wherein the wherein the charging protocolincludes discharging the battery pack such that the voltage of any onebattery in the battery pack does not fall below its minimum operationalvoltage after failure of a battery in the battery pack.
 7. The system ofclaim 6, wherein the charging protocol includes charging the batterypack to a charged pack voltage and discharging the battery pack to adischarged pack voltage, the charged pack voltage being the same beforeand after the failure of the battery, and the discharged pack voltagebeing the same before and after the failure of the battery.
 8. Thesystem of claim 7, wherein the capacity discharged from each batterywhen discharging from the charged pack voltage to the discharged packvoltage before failure of the battery is less than or equal toC_(m)(M−1)/(M+1), where M is the number of power sources in eachparallel group and C_(m) is the maximum operational capacity of abattery.
 9. The system of claim 1, wherein the charging protocolincludes charging the battery pack to a charged pack voltage that isless than a maximum operational voltage of the battery pack.
 10. Thesystem of claim 1, further comprising: a plurality of series groups,each series group connecting in series at least one of the power sourcesfrom each of the parallel groups.
 11. A battery system, comprising: abattery pack having a plurality of parallel groups connected in series,each parallel group including a plurality of power sources connected inparallel, each power source including a battery; and electronicsconfigured to discharge the battery pack according to a chargingprotocol configured such that the voltage of any one battery in thebattery pack does not fall below its minimum operational voltage afterfailure of a battery in the battery pack.
 12. The system of claim 11,wherein the electronics are configured to discharge the battery packwith the same charging protocol before failure of the battery and afterfailure of the battery.
 13. The system of claim 12, wherein the chargingprotocol includes discharging the battery pack to a discharged packvoltage, the discharged pack voltage being the same before and after thefailure of the battery.
 14. The system of claim 11, wherein each powersource consists of a battery.
 15. The system of claim 11, furthercomprising: a plurality of series groups, each series group connectingin series at least one of the power sources from each of the parallelgroups.
 16. A method, comprising: repeatedly charging a battery packaccording to a charging protocol configured such that the voltage of anyone battery in the battery pack does not exceed its maximum operationalvoltage after failure of a battery in the battery pack, the battery packhaving a plurality of parallel groups connected in series, each parallelgroup including a plurality of power sources connected in parallel, eachpower source including a battery.
 17. The method of claim 16, whereinthe charging protocol is executed by electronics.
 18. The method ofclaim 16, wherein the same charging protocol is employed before failureof the battery and after failure of the battery.
 19. The method of claim18, wherein the charging protocol includes charging the battery pack toa charged pack voltage, the charged pack voltage being the same beforeand after the failure of the battery.
 20. The method of claim 16,wherein each power source consists of a battery.
 21. The method of claim16, further comprising: repeatedly discharging the battery packaccording to the charging protocol and wherein the charging protocol isconfigured such that the voltage of any one battery in the battery packdoes not fall below its minimum operational voltage after failure of abattery in the battery pack.
 22. The method of claim 21, wherein thecharging protocol includes discharging the battery pack such that thebattery pack discharge is stopped upon the battery pack voltage fallingto a discharged pack voltage.
 23. The method of claim 16, wherein thecharging protocol includes charging the battery pack to a charged packvoltage and discharging the battery pack to a discharged pack voltage,the charged pack voltage being the same before and after the failure ofthe battery, and the discharged pack voltage being the same before andafter the failure of the battery.
 24. The method of claim 23, whereinthe capacity discharged from each battery when discharging from thecharged pack voltage to the discharged pack voltage before failure ofthe battery is less than or equal to C_(m)(M−1)/(M+1), where M is thenumber of power sources in each parallel group and C_(m) is the maximumoperational capacity of a battery.
 25. A method, comprising: repeatedlydischarging a battery pack according to a charging protocol configuredsuch that the voltage of any one battery in the battery pack does notfall below its minimum operational voltage after failure of a battery inthe battery pack, the battery pack having a plurality of parallel groupsconnected in series, each parallel group including a plurality of powersources connected in parallel, each power source including a battery.